1. Field of the Invention
The present invention relates to a method of on air registration of a cordless telephone with a base station.
The invention finds application in the second generation of cordless telephones, commonly known as (CT2) in which the transmission method employed is called `burst mode` transmission.
2. Description of Related Art
In burst mode transmission, the information to be transmitted is accumulated by a unit's transmitter, and transmitted in a `burst` to a receiving unit, after which the unit's transmitter is switched off, and the unit's receiver is switched on. The receiver is then expecting to receive a similar burst from the other unit. These bursts are transmitted and received by the two units on the same radio frequency.
Under the existing situation, if the user wishes to gain access to, for example a telepoint network, a user has to register to at least that network. The transmissions between the user and the network through free space is by virtue of a radio link used in accordance with what is commonly called the Common Air Interface. The Common Air Interface is a published document HPT1375 and is published by the Department of Trade and Industry, the last publication being May 1989. The Common Air Interface sets down the conditions which all users have to meet in order to communicate with their respective base stations. Each base station in the telepoint network is capable of receiving communications from a number of hand held user stations, and therefore, providing the user is within sufficient range to enable radio communication to occur between the user's handset and the base station, the base station can handle the call. The base station would typically interface with the public switched telephone network.
Registration of a handset to a network is achieved by using values of a link identification code.
The information that is loaded into the handset consists of:
1) 16 bits of a link identification code value, which is used when establishing link to identify the network or service required, PA1 2) 64 bits of a personal identification number value, which is an encrypted binary number, which together with the handset's own identity may serve to identify the handset and/or user with greater security. This personal identification number value is derived from a variety of numbers, and may include the handset's unique identity number, PA1 3) a nine bit value which is used to identify the home network, that is the network operator from whom the data is obtained, PA1 4) a 3 bit value, which Indicates to the network the class of service available to the handset, and PA1 5) up to 20 binary coded decimal digits (BCD) which could be used as an account number to which the call charges is to be billed.
All of the above data needs to be entered into the handset, which hitherto has been done manually. This results in a digit sequence to be dialed in to the handset by the user wishing to register with a network. The number of key strokes to be entered can be up to 66 digits, which is likely to be an error prone and tedious task for the user.
An additional number which is used during authentication for access to a telepoint network is also required, which is a four bit binary number (ZAP). This number is not entered by the user and is specifically barred from being entered by the user. This value can however be altered by messages over the radio link.
The use of the ZAP value causes some problems as it is one of the numbers used to calculate the personal identification number and in doing so the network has to assume a value for ZAP which can have one of 16 values. When a newly registered user tries to access a network for the first time, the authentication is likely to fail, because the assumed ZAP value is likely to be different from the actual value in the handset. This means that the network will have to instruct the handset to alter the ZAP value up to 15 times in order for authentication to be ultimately successful. This adds to network complexity and is a relatively time consuming task.
In summary, there are two problems associated with the existing method, the long, tedious and potentially error prone manual entry of data, and the increased network complexity due to the lack of knowledge of the ZAP values.